Ok, classes ended last week and my brain is way out of math shape. Right now I am contemplating how to show that the complements of this object

and of the complement of the object depicted in figure 3, are NOT homeomorphic.

I can do this in this very specific case; I am interested in seeing what happens if the “tangle pattern” is changed. Are the complements of these two related objects *always* topologically different? I am reasonably sure yes, but my brain is rebelling at doing the hard work to nail it down.

Anyhow, finals are graded and I am usually treated to one unusual student trick. Here is one for the semester:

Now I was hoping that they would say at which case the integral is translated to: which is easy to do.

Now those wanting to do it a more difficult (but still sort of standard) way could do two repetitions of integration by parts with the first set up being and that works just fine.

But I did see this: (ok, there are some domain issues here but never mind that) and we end up with the transformed integral: which can be transformed to by elementary trig identities.

And yes, that leads to an answer of which, upon using the triangle

Gives you an answer that is exactly in the same form as the desired “rationalization substitution” answer. Yeah, I gave full credit despite the “domain issues” (in the original integral, it is possible for ).

What can I say?

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I liked your first suggestion to solve the integral, i.e. by substituting . There are several books that are full of good integrals and “tricks” by which to solve them.

Comment by B. Doyle — May 29, 2016 @ 12:19 am

Correction –

Comment by B. Doyle — May 29, 2016 @ 12:20 am

maybe we can substitute \sqrt{x+1}=u.

Comment by xianyouhoule — June 12, 2016 @ 4:40 pm